Trevor J. Morgan

The unusual properties of high mass materials from coal-derived liquids☆

Abstract This short paper highlights the unusual properties of the high-mass material of coal liquids isolated by their insolubility in pyridine and solubility in NMP. The separation has been achieved by a column chromatography method. One gram quantity have been processed and near quantitative recovery of the sample as fractions has been achieved. This fractionation permitted recourse to a broad range of analytical methods, including some (e.g. 13 C NMR), which require large sample sizes. Multiple macro analyses have been undertaken, using elemental analysis, TGA proximate analysis, NMR and FT-ir in addition to the micro-analytical methods used previously—pyrolysis-gc-ms, SEC, UV–fluorescence, probe-ms and MALDI-ms. The fractions show increasing concentrations of large molecular mass material with increasing polarity of successive eluents used in the fractionation. Evidence from solid-state 13 C NMR and UV–fluorescence spectroscopy show progressive structural changes with increasing apparent molecular mass.

Characterization of Petroleum Asphaltenes by Size Exclusion Chromatography, UV-fluorescence and Mass Spectrometry

Abstract The molecular weight of petroleum asphaltenes remains the subject of debate. Our previous work using size exclusion chromatography with 1-methyl-2-pyrrolidinone (NMP) as eluent, combined with mass spectrometry and fluorescence spectroscopy has indicated molecular masses up to 40,000 u. The present work investigates the asphaltene fraction of Kuwaiti crude oil. The asphaltene was separated into several NMP-soluble fractions and an insoluble residue. The evidence from size exclusion chromatography (SEC) and UV-fluorescence spectroscopy (UV-F) shows that the molecular size range and the size of the aromatic chromophores increased with increasing insolubility in NMP. A steady increase in the sizes of the range of chromophores was shown by UV-fluorescence in going from the maltene fraction, via the asphaltene sample to the NMP-insoluble residue, using chloroform as solvent. Laser-desorption mass spectra showed very wide mass ranges for the whole asphaltene and the NMP-insoluble residue of asphaltenes, with a signal up to m/z 200,000 and slightly more ion intensity at high masses for the residue compared to that from the asphaltene.

Molecular mass ranges of coal tar pitch fractions by mass spectrometry and size-exclusion chromatography

A coal tar pitch was fractionated by solvent solubility into heptane-solubles, heptane-insoluble/toluene-solubles (asphaltenes), and toluene-insolubles (preasphaltenes). The aim of the work was to compare the mass ranges of the different fractions by several different techniques. Thermogravimetric analysis, size-exclusion chromatography (SEC) and UV-fluorescence spectroscopy showed distinct differences between the three fractions in terms of volatility, molecular size ranges and the aromatic chromophore sizes present. The mass spectrometric methods used were gas chromatography/mass spectrometry (GC/MS), pyrolysis/GC/MS, electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) and laser desorption time-of-flight mass spectrometry (LD-TOFMS). The first three techniques gave good mass spectra only for the heptane-soluble fraction. Only LDMS gave signals from the toluene-insolubles, indicating that the molecules were too involatile for GC and too complex to pyrolyze into small molecules during pyrolysis/GC/MS. ESI-FTICRMS gave no signal for toluene-insolubles probably because the fraction was insoluble in the methanol or acetonitrile, water and formic acid mixture used as solvent to the ESI source. LDMS was able to generate ions from each of the fractions. Fractionation of complex samples is necessary to separate smaller molecules to allow the use of higher laser fluences for the larger molecules and suppress the formation of ionized molecular clusters. The upper mass limit of the pitch was determined as between 5000 and 10,000 u. The pitch asphaltenes showed a peak of maximum intensity in the LDMS spectra at around m/z 400, in broad agreement with the estimate from SEC. The mass ranges of the toluene-insoluble fraction found by LDMS and SEC (400-10,000 u with maximum intensity around 2000 u by LDMS and 100-9320 u with maximum intensity around 740 u by SEC) are higher than those for the asphaltene fraction (200-4000 u with maximum intensity around 400 u by LDMS and 100-2680 u with maximum intensity around 286 u by SEC) and greater than values considered appropriate for petroleum asphaltenes (300-1200 u with maximum intensity near 700 u).

Structural characterization of products from fuel-rich combustion: An approach based on size exclusion chromatography

High molecular weight carbonaceous materials formed in the combustion of ethylene were collected from a premixed laminar flame operating under fuel-rich combustion conditions. Particulates collected from the flame were extracted with dichloromethane (DCM) to separate condensed species, soluble in DCM, from solid carbonaceous material (soot), insoluble in DCM. These samples were examined by size exclusion chromatography (SEC) using NMP as eluent, with detection by UV absorbance and light scattering. SEC of soot and related materials has provided a path to a more thorough characterization of these materials than has been hitherto available. The data show that there are step changes in structures from the small near-planar polycyclic aromatic hydrocarbon molecules, to large components with elution times corresponding to polystyrenes of mass about one million and to the very large species that are caught by the 20-nm filter. While the suggested molecular masses are enormous, to date no evidence could be found to show that these materials consist of aggregated smaller molecular structures.

Positive-Ion Electrospray Ionisation Mass Spectrometry of Acetone- and Acetonitrile-Soluble Fractions of Coal-Derived Liquids:

The acetone-soluble fraction of a coal tar pitch has been examined using positive ion electrospray ionisation (ESI), by infusion into the ESI stream. The acetonitrile-soluble fractions of a coal tar pitch, a coal digest and a low temperature coal tar have also been studied by high performance liquid chromatography/ESI mass spectrometry. In contrast to positive-ion ESI of proteins, which gives rise to multiply charged ions, this application to fossil fuels, petroleum asphaltenes and humic acids, appears to only give singly-charged ions. The major components of these samples, polycyclic aromatics that could be detected by gas chromatography/mass spectrometry, formed no ions in positive-ion ESI. The only ions detected were formed from azaarenes. Ions up to only m/z 500 or so were detected, although these fractions are known to contain higher-mass species, up to at least several thousand mass units. Fractions of the three samples [coal tar pitch, coal digest and a low temperature coal tar], insoluble in acetonitrile gave no satisfactory ESI spectra. The nitrogen contents of the fractions indicate that azaarenes become more prominent with increasing mass. However, these larger species could not be observed in the ESI mass spectra. Only some of the minor components of these samples could be observed. Size-exclusion chromatography and matrix-assisted laser desorption/ionisation mass spectrometry both indicate considerably larger molecules than those found by ESI-MS.

Estimation of the molecular mass range of the tar from pyrolysis of casein by gas chromatography-mass spectrometry, probe mass spectrometry and size exclusion chromatography with 1-methyl-2-pyrrolidinone as eluent

Casein has been pyrolysed to obtain a biochar (28.3% yield), with mostly meso- and macro-pore structure, and a liquid tar product of high yield (37.5%) with the balance as gas (20.9%) and water (13.3%). The elemental composition of the casein tar was: C 66.7%, H 8.3%, N 12.1% and O 12.9% (by difference). The tar sample has been characterised by mass spectrometry, gas chromatography (GC)/MS and heated-probe MS, to give molecular mass distributions for comparison with molecular mass ranges indicated by analytical-scale size-exclusion chromatography (SEC). The tar appeared to be completely soluble in 1-methyl-2-pyrrolidinone (NMP), the solvent used for SEC. It appeared to consist mostly of lower molecular mass fractions with elution times at 18–26 min. GC/MS analysis showed the presence of both aliphatic and aromatic nitrogen-containing components. Neither GC/MS nor heated-probe MS were able to detect more than about half the tar components.

Liquefaction: Thermal breakdown in the liquid phase

This chapter deals with the process of liquefaction, which is the thermal breakdown in the liquid phase. During the liquefaction process, materials extracted by the solvent and those detached from the solid coal matrix by the rupture of covalent bonds are released into the liquid phase. The chapter presents an outline of the general trends to be expected from coal liquefaction experiments and examines how the interplay between reaction chemistry and reactor design can affect observations made during bench scale experiments. For any given coal, the extractable material content prior to the covalent bond rupture stage is variable. It depends on the solvent used for extraction and the temperature. Based on this understanding, this chapter presents a conceptual integration of sample characterization with reactor design. The chapter also presents a review of methods for liquid product characterization. The integration of product characterization with reactor design leads to attempt a unified understanding of successive thermally driven events that bring about thermal breakdown in pyrolysis and liquefaction.

Pyrolysis of waste polypropylene and characterisation of tar

Waste polypropylene (PP) has been pyrolysed to obtain mainly a liquid tar product of high yield (83.5%) with the balance as gas (15.5%) and a little residue (1.0%). The elemental composition of the PP tar was: C: 87.1%, H: 12.6% and O+others: 0.4% (by difference). The tar samples have been characterised by gas chromatography/mass spectrometry, heated-probe mass spectrometry and laser desorption mass spectrometry (LD-MS), to give molecular mass distributions for comparison with molecular mass ranges indicated by size-exclusion chromatography (SEC). About 50% of the tar was soluble in 1-methyl-2-pyrrolidinone, the solvent used for SEC. It appeared to consist mostly of low molecular mass materials with elution time at 20–27 min. Mass ranges from SEC and LD-MS agreed approximately in showing the upper mass limit of the tar to be about 1200 u, consisting of aromatics, alkenes, dialkenes and only minor quantities of alkanes.

Elucidating transfer hydrogenation mechanisms in non-catalytic lignin depolymerization

Lignin undergoes catalytic depolymerization in the presence of a variety of transfer hydrogenation agents, however the mechanisms for non-catalytic depolymerization of lignin via transfer hydrogenation are not well understood; this makes process optimization difficult. Herein, for the first time a mechanism for this process is proposed. For the purposes of understanding the mechanisms involved in these non-catalytic lignin depolymerization processes, this study investigates the equilibrium system of formic acid, methyl formate and carbon monoxide, as agents for the depolymerization of lignin, in the presence of either water or methanol as solvents. In the methyl formate/water (at 300 °C) system, 73 wt% oil was produced which contained a significant amount of low molecular weight alkylphenols, with less than 1 wt% char produced. In aqueous media, the results showed that methyl formate maintains an equilibrium with formic acid which is itself in equilibrium with carbon monoxide. It was found that using either formic acid or methyl formate for non-catalytic transfer hydrogenation of lignin can produce high amounts of oil, and can be described as a two-stage mechanism. After 10 min of reaction at 300 °C, around a quarter of the formic acid is consumed via hydride transfer of the formate proton, preventing the condensation of lignin fragments. At the same time, approximately three quarters of the formic acid decomposes to carbon dioxide and carbon monoxide. Once the formic acid is consumed, the carbon monoxide was identified as the precursor to a reactive reductive reagent and was able to activate the proton of the water molecule preventing further condensation of the lignin fragments. It has been previously thought that transfer hydrogenation in lignin using formic acid occurs via the production of molecular hydrogen. Here it is demonstrated that formic acid reacts directly with the lignin, without this hydrogen formation. Therefore the key parameters for efficient transfer hydrogenation of the lignin to maximize bio-oil yield appear to involve controlling the reactions between lignin and formic acid, methyl formate or carbon monoxide under aqueous conditions, thereby reducing the reagent cost and loading while maintaining efficient lignin conversion.

Fossil fuels and renewables

This introductory chapter provides a brief outline of the material covered in this book. Two areas of research concerning the thermochemical processing of coal and lignocellulosic biomass have been described. The development of experimental methods for exploring the mechanics of thermal breakdown in lignocellulosic biomass and coal has been reviewed. The second area covers the development of methods for the analytical characterization of heavy hydrocarbon liquids, produced by the thermochemical reactions of solid fuels. The scope of the analytical work extends to the study of molecular mass distributions and the structural characteristics of petroleum-derived heavy fractions. The chapter provides a brief historical review of solid fuel utilisation and outlines recent trends in renewable and fossil fuel consumption.